1. Field of the Invention
The present invention relates generally to energy absorbers and energy absorption systems, and more particularly, to a failsafe magnetorheological damper for shock and vibration energy absorption systems employing a combination of permanent or switchable magnets with electromagnetic coils.
2. Description of Prior Art
The primary function of a shock and vibration protection system is to minimize the potential for equipment damage and/or personnel injury during shock and vibration loading. Such systems are important for vehicular applications, including aircraft, ground vehicles, marine vehicles, etc. Severe shock events may include harsh vertical or crash landings of aircraft, under body explosions of military ground vehicles, horizontal collisions of automobiles, and severe wave-to-hull impact of high speed watercraft. Lower amplitude shock and vibration tend to result from normal operation of such vehicles, including aircraft air loads or rotor loads, ground vehicles traversing rough terrain, etc. The severity of equipment damage and/or personnel injuries can be considerably minimized if the vehicles are equipped with shock and vibration protection systems.
Most current shock and vibration protection systems are passive, in that they cannot automatically adapt their energy absorption as a function of payload weight or as a function of real-time environmental measurements such as shock level, impact velocity, vibration levels, etc. Moreover, some energy absorbers are essentially rigid and do not stroke until the load reaches a tuned threshold. Because of this, these systems provide no isolation of vibration. This motivates the development of a shock and vibration protection system that utilizes an electronically adjustable adaptive energy absorber that can provide adaptive energy absorption for enhanced crashworthiness as well as vibration mitigation.
Magnetorheological (MR) technology is particularly attractive for shock and vibration protection systems as an MR fluid based device can offer an innovative way to achieve what is effectively a continuously adjustable energy absorber, in combination with a real-time feedback controller, can automatically adapt to payload weight and respond to changing excitation levels. With its ability to smoothly adjust its load-stroke profile, MR energy absorbers can provide the optimum combination of short stroking distance and minimum loading while automatically adjusting for the payload weight and load level. Furthermore, MR energy absorbers offer the unique ability to use the same system for vibration isolation.
For example, adaptive energy attenuation (EA) devices for helicopter seats can provide enhanced crash safety by adjusting their stroking load in response to both varying occupant weight and impact severity. This makes it possible to minimize shock load induced injury across a range of occupants and crash severities. Hiemenz, G. J., Choi, Y. T. and Wereley, N. M., “Semi-Active Control of a Vertical Stroking Helicopter Crew Seat for Enhanced Crashworthiness”, Journal of Aircraft, AIAA, Vol. 4, No. 3, May-June 2007, pp. 1031-1034. Even during normal operation whole body vibration (WBV) has become a key concern due to associated chronic injuries, fatigue, and loss of situational awareness. Harrer, K. L., Yniguez, D., Majar, M., Ellenbecker, D., Estrada, N., and Geiger, M., “Whole Body Vibration Exposure for MH-60S Pilots”, Proceedings of the Forty Third Annual SAFE Association Symposium, Salt Lake City, Utah, Oct. 24-26, 2005, pp. 303-314.
MR energy absorbers offer a promising technology to address both adaptive crash attenuation and vibration isolation. By modulating the MREA force in real-time based upon sensor inputs (i.e., sink rate, piston velocity, stroke), these systems minimize the load transmitted to the occupant by safely utilizing the full available stroke of the seat. By modulating the MREA force in real-time based upon sensor inputs (i.e., sink rate, piston velocity, stroke) these systems are able to attenuate crash loads for a wide range of occupant weights and crash severity. MR energy absorbers can provide the additional benefit of occupant protection against vibration. Many MR energy absorbers for shock and vibration isolation mounts have been disclosed such that the damping level can be controlled in feedback by applying a magnetic field (U.S. Pat. No. 5,277,281 to J. D. Carlson et al., U.S. Pat. No. 6,279,700 to H. Lisenkser et al., U.S. Pat. No. 6,311,810 to P. N. Hopkins et al., U.S. Pat. No. 6,694,856 to P. C. Chen and N. M. Wereley, U.S. Pat. No. 6,953,108 to E. N. Ederfass and B. Banks, U.S. Pat. No. 6,481,546 to M. L. Oliver and W. C. Kruckemeyer, and U.S. Pat. No. 6,983,832 to C. S. Namuduri et al). See also, U.S. Pat. No. 6,694,856 issued Feb. 24, 2004 to Chen et al. which includes test data obtained from a COTS Lord Rheonetics® MR damper including force vs. piston behavior.
However, a key challenge in vehicular applications involving MR energy absorbers, such as helicopter seats, is the device weight and size. MR energy absorbers must have a large controllable range, stroke, and bandwidth to provide adaptation to payload weight, shock energy, speed, and required energy absorption. The size and weight of conventional linear-piston MR damper designs for such applications can make their use prohibitive. Hence, the development of more compact, lighter weight MR devices with the capability to adapt to shock and vibration conditions is of great interest.
Another key challenge is the requirement for fail-safe performance should vehicle power not be available during a crash. The concern of fail-safe performance arises because MREAs are typically in their low-force condition when electrical current is not supplied. If there is a loss in power, the device will operate in its off-state (passive) condition and will passively absorb energy, but will provide little or no crash protection.
The present invention provides a failsafe Adaptive MR Energy Absorber (FAMEA) for helicopter and other vehicle seats that is lightweight and compact.